Hearing aid users have been reported to have poorer ability to localize sound sources when wearing their hearing aids than without their hearing aids. This represents a serious problem for the mild-to-moderate hearing impaired population.
Furthermore, hearing aids typically reproduce sound in such a way that the user perceives sound sources to be localized inside the head. The sound is said to be internalized rather than being externalized. A common complaint for hearing aid users when referring to the “hearing speech in noise problem” is that it is very hard to follow anything that is being said even though the signal to noise ratio (SNR) should be sufficient to provide the required speech intelligibility. A significant contributor to this fact is that the hearing aid reproduces an internalized sound field. This adds to the cognitive loading of the hearing aid user and may result in listening fatigue and ultimately that the user removes the hearing aid(s).
Recently, new hearing aids have been disclosed with improved localization of sound sources, i.e. the new hearing aids preserve information of the directions of respective sound sources in the sound environment with relation to the orientation of the head of the wearer of the hearing aid, see EP 2 750 410 A1, EP 2 750 411 A1, and EP 2 750 412 A1.
Improved sound source localization enables hearing aid users to utilize the cocktail party effect, i.e. the user is able to focus the auditory attention on a selected sound source while suppressing all other sounds, e.g. to focus on a single conversation in a noisy room at a party.
However, in complex listening situations with adverse signal to noise ratios (SNR) some hearing impaired people cannot use spatial cues to segregate between different sound sources and focus on a selected sound source and suppress everything else. Other solutions have to be developed for this situation and/or for this subpopulation.
One known way of alleviating this problem is to apply SNR enhancing techniques, such as directionality. Directional systems operate to suppress signal energy from all other directions than a target direction. This requires that interfering sound has a directional nature; however, in complex listening situations, such as in a restaurant, the hearing aid user experiences interference from diffuse noise. Diffuse noise is, or approximately is, spatially white, i.e. the signal recorded in the noise field is uncorrelated with any other signal record at a different location. The number of microphones in a hearing aid system is typically not sufficient to efficiently suppress diffuse noise. Therefore, directional systems have limited effect for these types of listening situations.
Another complaint when applying directionality is that the listener loose environmental awareness.